1. Field of the Invention
The present invention relates to a field of drive control of a display apparatus. Specifically, the present invention relates to a color signal correction circuit, a color signal correction apparatus, a color signal correction method, and a color signal correction program, which are used for color signal correction in a display apparatus, and also relates to a display apparatus in which such color signal correction can be realized.
2. Description of the Related Art
The performance of a color display device used for an electronic apparatus or the like has been improving on a year-by-year basis. This trend is found not only in a large size display device incorporated in a liquid crystal TV, or the like, but also in a small size display device incorporated in a portable apparatus, such as a portable telephone, a portable game apparatus.
For example, in a conventional portable game apparatus, an image is displayed based on a low-resolution color-scale color signal, such as an animation image. However, recently, consumers have demanded high-quality color image displays, for example, of an image which looks like a natural picture where an object within a three-dimensional space is expressed with shadows. For the purpose of satisfying such a demand, it is necessary to provide some means to allow a color signal of higher-resolution color-scale (multiple color-scale levels) to be used in a display apparatus and a control circuit thereof.
Herein, a xe2x80x9ccolor signalxe2x80x9d refers to display data (color component data), such as an image displayed on pixels arranged in a matrix over a display apparatus, i.e., a color-scale representation value which is used for controlling the brightness of the pixels.
A conventional liquid crystal display apparatus has the following structure. FIG. 11 is a block diagram showing the structure of a conventional liquid crystal display apparatus. The liquid crystal display apparatus 101 includes: a liquid crystal display module 7; an external host system 8; and a system bus 9 which connects the liquid crystal display module 7 and the external host system 8. The liquid crystal display module 7 includes a liquid crystal display panel unit 11, a liquid crystal driving controller 12 (hereinafter xe2x80x9cLCDCxe2x80x9d), and a display memory 13. The external host system 8 includes a CPU 15; a system memory 16, and an I/O system 17.
For example, the liquid crystal display panel unit 11 includes: a TFT-type liquid crystal panel having pixels arranged in a matrix; a source driver for applying to a TFT source line of the liquid crystal panel a color-scale representation voltage, which is determined based on image display data generated for driving the liquid crystal panel; a gate driver for applying a scan control signal to a TFT gate line of the liquid crystal panel; and a liquid crystal driving voltage generation circuit for generating the color-scale representation voltage. In the case where the liquid crystal display panel unit 11 includes a STN-type liquid crystal panel, a segment driver and a common driver are used in place of the above source and gate drivers.
The LCDC 12 is a controller circuit which generates, under the control of the external host system 8, a control signal for controlling the source driver and the gate driver and an image display signal (data) to be supplied to the source driver. The LCDC 12 further includes: an interface section 21 for transmission of signals and data with the external host system 8 and the display memory 13; and a signal processing section 22 for reading image display data from the display memory 13 and generating a control signal to be supplied to the source driver in the liquid crystal display panel unit 11.
The LCDC 12 outputs: a transfer clock signal for transferring image display data; a source driver start pulse signal (horizontal synchronization signal) for controlling the start of transfer of the image display data based on the unit of a horizontal synchronization period; a gate driver start pulse signal (vertical synchronization signal) for controlling the start of scanning of a scan control signal; and a control signal, such as an alternating signal used for performing an alternating driving of the liquid crystal panel.
The external host system 8 is a commonly employed CPU system which transfers the image display data, which has been externally input through the I/O system 17, to the liquid crystal display panel unit 11, and controls the liquid crystal display module 7 via the system bus 9.
Recently employed liquid crystal display panel units include a TFT-type liquid crystal display panel unit which performs color-scale representation corresponding to image display data consisting of 18 bits in total. In this liquid crystal display panel unit, color image display data is data of 64 color-scale levels (=26) where 6 bits are allocated to each of R (red), G (green), and B (blue) pixels, each of which corresponds to 1 dot. The liquid crystal display module including this liquid crystal display panel unit is controlled using a CPU system which includes a commonly-employed, general purpose control processor, rather than a special purpose control processor, as an external host system. This is because the CPU system which includes the commonly-employed, general purpose control processor is less expensive, and can be used for various purposes.
The bit number of data which can be used in such a general purpose control processor is a multiple of 8 (i.e., 4), i.e., 8 bits, 16 bits, 24 bits, 32 bits, etc.
As of now, image display data consisting of 16 bits can express a color image by 65536 (=216) colors. In a color data pattern used for this image display data, a 5-6-5 format is generally employed. In the 5-6-5 format, as color-scale representation values, 5 bits are allocated to R, 6 bits to G, and 5 bits to B, so as to obtain image display data consisting of 16 bits in total.
In a TFT-type liquid crystal display panel unit, as described above, 6 bits are allocated as a color-scale representation value to each of R, G, and B, so as to obtain a uniform bit structure. That is, image display data to be processed consists of 18 bits in total.
Thus, in the liquid crystal display module 7 shown in FIG. 11, if image display data output from the external host system 8 and input to the LCDC 12 through the system bus 9 has a 16-bit structure, this data must be converted or corrected in the signal processing section 22 of the LCDC 12 into image display data consisting of 18 bits in total, where 6 bits are allocated as a color-scale representation value to each of R, G, and B.
Thus, in the signal processing section 22 of the LCDC 12, in order to obtain conformity between image display data consisting of 18 bits and image display data consisting of 16 bits, the image display data of 16 bits is subjected to color-scale correction such that 5-bit image data allocated to each of R-pixel and B-pixel is expanded to 6-bit image display data.
Conventional techniques of such color-scale correction are explained below:
(1) LSB (Least Significant Bit) Fixed Method
In this method, 1 bit is newly added as a least significant bit (LSB) to 5-bit image display data so as to obtain 6-bit data, and this new LSB is set to xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d by default.
(2) MSB (Most Significant Bit) Repetition Method
In this method, 1 bit is newly added as a least significant bit (LSB) to 5-bit image display data so as to obtain 6-bit data, and a value equal to data of the most significant bit is set as data of the least significant bit (LSB).
(3) Color-Scale Palette Method
In this method, the relationship between 5-bit image display data and 6-bit image display data is established in the form of a palette (also referred to as a xe2x80x9clook up table (LUT)xe2x80x9d or a xe2x80x9cconversion tablexe2x80x9d). When certain image display data is input, image display data corresponding to the input image display data is output.
However, all of the above methods have a problem in color reproducibility (reproducibility of color-scale representation). Hereinafter, problems in each method are described, while considering an image example consisting of 8xc3x978 pixels. Specifically, how to convert color component data in a color-scale correction process, where color component data (color-scale representation data) of 5-bit image display data is expanded so as to be 6-bit image display data, is described.
FIG. 12 shows an example of a display pattern of image display data (original image data) consisting of 5 bits, which is input to the LCDC 12. In FIG. 12, each circle represents a single pixel, and a value shown in each circle is a color component data value (color-scale representation data value) which corresponds to a pixel. This also applies to the display pattern diagram which will be described later. In this example, a color component is represented by a 5-bit value, and therefore, 32 (25=32) different values, i.e. xe2x80x9c00hxe2x80x9d to xe2x80x9c1Fhxe2x80x9d (xe2x80x9chxe2x80x9d means that the value is represented by a hexadecimal number), can be displayed. In the example illustrated in FIG. 12, from a pixel at the left upper corner (coordinate (X=0, Y=0) in FIG. 12) to a pixel at the right lower corner (coordinate (X=7, Y=7)), 32 values from xe2x80x9c00hxe2x80x9d to xe2x80x9c1Fhxe2x80x9d are arranged such that the value of the pixels increases every two pixels.
In this example, value xe2x80x9c00hxe2x80x9d in 5-bit image display data or 6-bit image display data is data which corresponds to the darkest pixel in the display. Value xe2x80x9c1Fhxe2x80x9d in 5-bit image display data is data which corresponds to the brightest pixel in the display. Value xe2x80x9c3Fhxe2x80x9d in 6-bit image display data is data which corresponds to the brightest pixel in the display.
1. Color-Scale Correction Based on LSB Fixed Method
FIGS. 13 and 14 are display pattern diagrams obtained after the original image data of FIG. 12 has been subjected to color-scale correction based on the LSB fixed method. First, an example where xe2x80x9c0xe2x80x9d data is added to the LSB of color component data of the original image so that the color component data is color-scale-corrected (expanded) so as to be 6-bit data, is described. In the color-scale correction based on this method, the brightest value xe2x80x9c1Fhxe2x80x9d at coordinate (X=6, Y=7) in the 5-bit representation of FIG. 12 is converted into value xe2x80x9c3Ehxe2x80x9d in FIG. 13 (see hatched circles). However, as described above, xe2x80x9c3Fhxe2x80x9d is data corresponding to the brightest pixel in the display of 6-bit representation. Thus, in this conversion method, the brightest point which can be displayed in the display panel cannot be displayed.
Next, another case where color-scale correction is performed by adding xe2x80x9c1xe2x80x9d data to the LSB of the color component in the original image so that the image is expanded into a 6-bit representation, is described. In the color-scale correction based on this method, the darkest pixel value xe2x80x9c00hxe2x80x9d at coordinate (X=0, Y=0) in the 5-bit representation of the original image data shown in FIG. 12 is converted into value xe2x80x9c01hxe2x80x9d in FIG. 14 (see hatched circles). However, as described above, xe2x80x9c00hxe2x80x9d is data corresponding to the darkest pixel in the display of the 6-bit representation. Thus, in this conversion method, the darkest point which can be displayed in the display panel cannot be displayed.
Further, in the case of the LSB fixed method, as illustrated in FIGS. 13 and 14, in any of the above color-scale correction methods, the number of types of data which can be displayed after color-scale correction is only 32 (32 color-scale level display). That is, in any of the above methods, the 6-bit display performance of the display panel (26=64 color-scale level display) is not fully used.
2. Color-Scale Correction Based on MSB Repetition Method
FIG. 15 is a display pattern diagram obtained after the original image data of FIG. 12 has been subjected to color-scale correction based on the MSB repetition method. In this example, hatched pixels (at coordinates (X=7, Y=3) and (X=0, Y=4)) in FIG. 15 are considered. In the original image data (5-bit representation) in FIG. 12, these two pixels have consecutive values, 0Fh (01111) and 10h (10000). However, through color-scale correction (bit expansion conversion), these values are converted into largely discrete values, 1Eh (011110) and 21h (100001).
That is, significantly discrete points are caused in a gradual brightness variation pattern. This method is disadvantageous in that discrete points are caused in a gradual brightness variation, although the brightest and darkest points within the performance range of the display panel, which cannot be displayed using the LSB fixed method, can be displayed.
Further, even in the case of the MSB repetition method, the number of types of data which can be displayed after color-scale correction is only 32 (32 color-scale level display). That is, even in this method, the 6-bit display performance of the display panel is not fully used.
As described above, in the MSB repetition method is and the LSB fixed method, characteristics of an image are not considered when the image is subjected to a difference bit expansion process, and the expansion process is performed in a simple manner. Thus, in such methods, the display performance that the display panel originally has cannot be fully used.
3. Color-Scale Correction Based on Palette Method
FIG. 16A is a display pattern diagram obtained after the original image data of FIG. 12 has been subjected to color-scale correction based on the palette method. FIG. 16B is an example of a palette.
Consider color-scale correction where 5-bit image display data of pixels at coordinates (X=5, Y=7) and (X=6, Y=7) of the original image data (FIG. 12) are converted to 6-bit image display data of FIG. 16A. In FIG. 12, the values of image display data of these pixels are consecutive values. However, through color-scale correction, these values are converted into discrete values by the values set in the palette of FIG. 16B (i.e., the difference of the values of these pixels is largely increased after conversion in comparison to that of other adjoining pixels). That is, significantly discrete points are caused in a gradual brightness variation pattern.
The palette method is characterized in that discrete points can be freely selected, whereas such selection cannot be performed in the MSB repetition method. However, even in this method, the number of types of data included in the palette is only 32. That is, even in this method, the 6-bit display performance of the display panel cannot be fully utilized.
Even though the color-scale palette method has flexibility such that the values in the palette can be freely changed, and therefore, a user can freely set color-scale expression parameters, such as xcex3-correction, or the like, once the values have been set, such a setting of values is applied to all displays. Thus, it is necessary to set the palette according to the type of an image to be displayed, e.g., a natural image, a graphic image, an animation image, etc. Accordingly, such an additional setting labor imposes a burden on a user.
Even if the palette is set according to the type of an image to be displayed, the above-described problem is not eliminated, i.e., the display performance of the display panel cannot be fully utilized.
Thus, as described above, the above conventional techniques bear a problem that high-quality color image data which fully utilizes the high color-scale display performance of a display apparatus cannot be obtained without imposing a burden on a user or without being dependent on an image to be displayed.
The present invention includes the following structures as means for solving the above problems.
(1) There is provided a color signal correction circuit for correcting a color signal which displays data on each pixel of a display apparatus arranged in a matrix, comprising: a color signal input section for inputting a color signal of N bits (N is a natural number); a color signal data storage section for storing a first color signal corresponding to a predetermined pixel, a second color signal corresponding to a first adjacent pixel which is adjacent to the predetermined pixel, and a third color signal corresponding to a second adjacent pixel which is adjacent to the predetermined pixel at the opposite side with respect to the first adjacent pixel, which are input to the color signal input section; an addition section for adding the second color signal and the third color signal to obtain addition value data; a duplication section for duplicating the first color signal to obtain duplicated color signal data; a first comparison section for subtracting the duplicated color signal data from the addition value data to obtain a difference value; a first LSB determination section for determining an LSB according to the difference value; and a color signal generation section for adding N higher order bits of the duplicated color signal data and the LSB, so as to generate a color signal of (N+1) bits.
In the color signal correction circuit having such a structure, in order to correct a color signal which displays data on each pixel of the display apparatus arranged in a matrix, the color signal data storage section stores a first color signal corresponding to a predetermined pixel, a second color signal corresponding to a first adjacent pixel which is adjacent to the predetermined pixel, and a third color signal corresponding to a second adjacent pixel which is adjacent to the predetermined pixel at the opposite side with respect to the first adjacent pixel, which are included in a color signal of N bits input to the color signal input section. The addition section adds the second color signal and the third color signal to obtain addition value data. The duplication section duplicates the first color signal to obtain duplicated color signal data. The first comparison section subtracts the duplicated color signal data from the addition value data to obtain a difference value. The color signal generation section adds the LSB determined by the first LSB determination section according to the difference value and N higher order bits of the duplicated color signal data, so as to generate a color signal of (N+1) bits.
Thus, color signal correction is performed on a color component of a color image using a simple circuit so as to obtain a color quality with smooth gradation, whereby the color resolution of the color image can be improved. A value of a low-order bit, which is rounded down in unexpanded data, is subjected to an arithmetic operation and comparison processing, and restored by estimation, As a result, image display with a high quality can be realized. It should be noted that xe2x80x9cLSBxe2x80x9d is an abbreviation of a Least Significant Bit.
(2) If the difference value is equal to or smaller than 0, the first LSB determination section sets the LSB to 0; and if the difference value is greater than 0, the first LSB determination section sets the LSB to 1.
In such a structure, if the difference value between the addition value data obtained by adding the second and third color signals by the addition means, and the duplicated color signal data obtained by duplicating the first color signal by the duplication section, is equal to or smaller than 0, the first LSB determination section sets the LSB to 0; and if the difference value is greater than 0, the first LSB determination section sets the LSB to 1. Thus, color signal correction can be performed while achieving high color reproducibility.
(3) There are provided a second comparison section for comparing the difference value with a predetermined reference value, and a second LSB determination section for setting the LSB to 0 when the difference value is equal to or greater than the predetermined reference value, and for setting the LSB to 1 when the difference value is smaller than the predetermined reference value.
In the color signal correction circuit having such a structure, the difference value between the addition value data obtained by adding the second and third color signals by the addition means and the duplicated color signal data obtained by duplicating the first color signal by the duplication section is compared with a predetermined reference value. The second LSB determination section sets the LSB to 0 when the difference value is equal to or greater than the predetermined reference value, and sets the LSB to 1 when the difference value is smaller than the predetermined reference value. Thus, color signal correction can be performed on an image having a sharp outline without blurring the outline, and the color resolution of the image can be improved.
(4) There is provided a selection section for selecting one of the LSB determined by the first LSB determination section and the LSB determined by the second LSB determination section.
In the color signal correction circuit having such a structure, a selection section selects one of the LSB determined by the first LSB determination section and the LSB determined by the second LSB determination section. With such an arrangement, the LSB can be selected according to the type of an image on which color signal correction is to be performed.
(5) The difference value obtained when an increase in the percentage of the number of corrected pixels stops or almost stops is used as the predetermined reference value.
In the color signal correction circuit having such a structure, the difference value obtained when an increase in the percentage of the number of corrected pixels stops or almost stops is used as the predetermined reference value which is to be compared with the difference value by the second comparison section. Thus, optimum color signal correction can be performed on various types of images, and the color resolution of the image can be improved. (6) The predetermined reference value is 7.
In this structure, the predetermined reference value which is to be compared with the difference value by the second comparison section is 7. Thus, even in the case where color signal correction is performed on an image representing an outline portion of a face or character which includes a portion where the brightness varies in a discrete manner, the outline portion is not blurred, and image correction can be performed while maintaining the sharp outline.
(7) There is provided a color signal correction apparatus comprising the color signal correction circuit of any of above paragraphs (1) to (6), wherein in color image data including a plurality of types of color signals, correction is performed on at least one of the plurality of types of color signals.
A color signal correction apparatus having such a structure includes the color signal correction circuit of any of above paragraphs (1) to (6), wherein at least a correction process is performed on one of a plurality of types of color signals. Thus, there is provided a color signal correction apparatus which performs color signal correction on a color component of a color image using a simple circuit so as to obtain a color quality with no uneven gradation, whereby the color resolution of the color image can be improved.
(8) The plurality of types of color signals include color signals for R-, G-, B-pixels.
In this structure, the plurality of types of color signals, which are input as color image data for each of the R-, G-, B-pixels, are corrected. Thus, the color resolution of the color image can be improved for each of the color components of the color image.
(9) There is provided a color signal correction method for correcting a color signal which displays data on each pixel of a display apparatus arranged in a matrix, comprising: a color signal input step of inputting a color signal of N bits (N is a natural number); a color signal data storage step of storing a first color signal corresponding to a predetermined pixel, a second color signal corresponding to a first adjacent pixel which is adjacent to the predetermined pixel, and a third color signal corresponding to a second adjacent pixel which is adjacent to the predetermined pixel at the opposite side with respect to the first adjacent pixel, which are input to the color signal input step; an addition value calculation step of adding the second color signal and the third color signal to obtain addition value data; a duplicated value calculation step of duplicating the first color signal to obtain duplicated color signal data; a first comparison step of obtaining a difference value between the addition value data and the duplicated color signal data; a first LSB determination step of determining an LSB according to the comparison result of the first comparison step; and a color signal generation step of adding N higher order bits of the duplicated color signal data and the LSB, so as to generate a color signal of (N+1) bits.
In this structure, a color signal is corrected by performing the following steps: a color signal input step of inputting a color signal of N bits (N is a natural number); a color signal data storage step of storing a first color signal corresponding to a predetermined pixel, a second color signal corresponding to a first adjacent pixel which is adjacent to the predetermined pixel, and a third color signal corresponding to a second adjacent pixel which is adjacent to the predetermined pixel at the opposite side with respect to the first adjacent pixel, which are input to the color signal input step; an addition value calculation step of adding the second color signal and the third color signal to obtain addition value data; a duplicated value calculation step of duplicating the first color signal to obtain duplicated color signal data; a first comparison step of obtaining a difference value between the addition value data and the duplicated color signal data; a first LSB determination step of determining an LSB according to the comparison result of the first comparison step; and a color signal generation step of adding N higher order bits of the duplicated color signal data and the LSB, so as to generate a color signal of (N+1) bits.
Thus, there is provided a method which can perform color signal correction on a color component of a color image so as to obtain a color quality with no uneven gradation, whereby the color resolution of the color image can be improved.
(10) There is provided a color signal correction program which instructs a computer to execute the following steps: a color signal input step of inputting a color signal of N bits (N is a natural number); a color signal data storage step of storing a first color signal corresponding to a predetermined pixel, a second color signal corresponding to a first adjacent pixel which is adjacent to the predetermined pixel, and a third color signal corresponding to a second adjacent pixel which is adjacent to the predetermined pixel at the opposite side with respect to the first adjacent pixel, which are input to the color signal input step; an addition value calculation step of adding the second color signal and the third color signal to obtain addition value data; a duplicated value calculation step of duplicating the first color signal to obtain duplicated color signal data; a first comparison step of obtaining a difference value between the addition value data and the duplicated color signal data; a first LSB determination step of determining an LSB according to the comparison result of the first comparison step; and a color signal generation step of adding N higher order bits of the duplicated color signal data and the LSB, so as to generate a color signal of (N+1) bits.
In this structure, a color signal is corrected by allowing a computer to execute a program including the following steps: a color signal input step of inputting a color signal of N bits (N is a natural number); a color signal data storage step of storing a first color signal corresponding to a predetermined pixel, a second color signal corresponding to a first adjacent pixel which is adjacent to the predetermined pixel, and a third color signal corresponding to a second adjacent pixel which is adjacent to the predetermined pixel at the opposite side with respect to the first adjacent pixel, which are input to the color signal input step; an addition value calculation step of adding the second color signal and the third color signal to obtain addition value data; a duplicated value calculation step of duplicating the first color signal to obtain duplicated color signal data; a first comparison step of obtaining a difference value between the addition value data and the duplicated color signal data; a first LSB determination step of determining an LSB according to the comparison result of the first comparison step; and a color signal generation step of adding N higher order bits of the duplicated color signal data and the LSB, so as to generate a color signal of (N+1) bits.
Thus, there is provided a color signal correction program which can perform color signal correction on a color component of a color image so as to obtain a color quality with no uneven gradation, whereby the color resolution of the color image can be improved.
(11) There is provided a display apparatus comprising the color signal correction circuit of any of above paragraphs (1) to (6) or the color signal correction apparatus of above paragraph (7) or (8).
In this structure, a display apparatus includes the color signal correction circuit of any of above sections (1) to (6), or the color signal correction apparatus of above section (7) or (8). Thus, the display apparatus can perform color signal correction on a color component of a color image using a simple circuit so as to obtain a color quality with no uneven gradation, whereby the color resolution of the color image can be improved.
(12) There is provided a display apparatus comprising a control section for executing the color signal correction program of above section (10).
A display apparatus having such a structure includes a control section for executing the color signal correction program of above section (10). Thus, the display apparatus can execute the color signal correction program to perform color signal correction on a color component of a color image using a simple circuit so as to obtain a color quality with no uneven gradation, whereby the color resolution of the color image can be improved.
Thus, the invention described herein makes possible the advantages of (i) providing a color signal correction circuit, a color signal correction apparatus, a color signal correction method, a color signal correction program, and a display apparatus, which can perform correction of color image data in a manner optimum to a gradually-varying color image data characteristic; and (ii) providing a color signal correction circuit, a color signal correction apparatus, a color signal correction method, a color signal correction program, and a display apparatus, which can perform correction of color image data in a manner optimum to a sharp color image data characteristic which varies in a non-gradual manner, e.g., a characteristic seen in specific image data, such as character data.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.